Firefly Effect Puts the Glow in New LED Bulb Tech

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Fireflies' green-yellow flashes are one of the simplest pleasures
of summer. Generations of kids have dreamed of lighting backyards
with jars full of them. And someday it may be possible to say
you've got a light full of fireflies — or at least a
firefly-inspired bulb.

New research has found that
LEDs that use firefly-inspired lenses need less energy to
shine brighter. Scientists have developed a lens for LEDs that is
etched with tiny dots, similar to how a
firefly's "lantern " is covered in tiny ridges. The lens
allows 98 percent of light to pass through it, which is
significantly better than a traditional lens, and an improvement
similar to coating a lens with an expensive anti-reflective
coating.

Ki-Hun Jeong of the Korea Advanced Institute of Science and
Technology and colleagues studied firefly abdomens under a
scanning electron microscope. They found the lantern part of the
abdomens — where the light is produced — is made of three layers,
and bears a striking resemblance to a standard LED bulb.

A standard LED is made of a reflective "cup" and a lens
sandwiching the light source. Similarly, a firefly's lantern is
made of a reflective layer, a light-emitting layer and a cuticle
layer, or exoskeleton, covered in tiny ridges. Compared to the
rest of the firefly's
exoskeleton, the ridges on the parts of the bug's abdomen
where light shone through were much more ordered.

Jeong found that the ridges helped the firefly's particular
wavelength of light pass through the firefly's lantern more
effectively, so they tried etching similar patterns into plastic.
Sure enough, creating a similar pattern of dots on an LED lens
allowed more light to pass through.

The technique could be used to boost light for camera phone
screens or flashes, car headlights, or even just residential
lighting, the researchers say.

The inspiration isn't an exact case of borrowing from Mother
Nature, as the manmade LED lens is much more regular and ordered
than a firefly's behind. The researchers used nanopillars packed
into the shape of a honeycomb, rather than the firefly's long
ridges. But just like a real firefly, the patterns seemed to work
best when the light had a wavelength of 560 nanometers, or the
familiar yellow-green glow of a lightning bug.

That doesn't necessarily mean that we'll all be carrying around
firefly-colored lanterns. The nanostructures could be tweaked to
boost different wavelengths, Jeong said. "Transmittance is very
sensitive to the shape of nanostructures,” he added. “The
physical dimension can be more optimized for a specific
wavelength of light."

The research appears in today's (Oct. 29) issue of Proceedings of
the National Academy of Sciences.